Natural gas dehydration
Before entering distribution pipelines, natural gas needs to be dried to prevent pipeline corrosion and blocking of valves by solid hydrates. In USA maximum allowed moisture level is in general 7 lbs / MMSCF. In Canada this is 4 lbs / MMSCF.
There are multiple technologies to dry natural gas below the maximum allowed level, like glycol, molsieve, membrane and refrigeration drying. Glycol and molsieve drying require handling of nasty chemicals and refrigeration is energetically not favoured. Membrane drying is a chemical-free solution with good energy-economics.
The membranes that are used for natural gas dehydration are highly permeable for moisture and exhibit low permeation for hydrocarbons. Membrane treatment results in removal of moisture (together with CO2 and H2S), leaving pure hydrocarbons as product gas.
Feed gas = Raw natural gas
Retentate gas = Purified natural gas, mainly CH4
Permeate gas = H2O